Tap changing system



Dec. 27, 1949 1.. F. BLUME ET AL TAP CHANGING SYSTEM Filed April 17, 1946 Inventor's: Louus F Blume, Salvatore Minnec'l,

by Their Attorney.

Patented Dec. 27, 1949 TAP CHANGING SYSTEM Louis F. Blumc and Salvatore Minneci, Pittsfield, Mass., assignors to General Electric Company, a corporation of New York Application April 17, 1946, Serial No. 662,795

8 Claims. 1

This invention relates to electric circuits and more particularly to improvements in load-ratiocontrol circuits.

As here used the term load-ratio-control means the control or variation of the ratio of a transformer while it is under load by changing tap connections to at least one of its windings. In such circuits there is at least one switch or contactor which performs an arcing or current interrupting duty and it is this arcing duty contactor which usually has the shortest operating life of any part of the circuit, that is to say, it requires more frequent servicing than any other part of the circuit, with the result that it is usually necessary to shut down the transformer periodically for the purpose of servicing the arcing contactor.

In accordance with the present invention there is provided a novel load-ratio-control circuit in which the arcing duty is divided up among a plurality of switches or contactors and in which the major part of the arcing duty is performed by a switch which is connected into the circuit by way of an auxiliary insulating transformer. This makes it possible to select the ratio of the insulating transformer such .as to give optimum current and voltage values to be ruptured by the arcing duty contactor. Furthermore, the arcing duty contactor, being in a separate circuit which is insulated from the main circuit by means of the insulating transformer, can be made readily accessible from outside the transformer and it can be serviced and even replaced while the main transformer is in operation.

An object of the invention is to provide a new and improved electric circuit.

Another object of the invention is to provide a new and improved load-ratio-control circuit.

A further object of the invention is to provide a new and improved arcing duty switching arrangement for load-ratio-control systems.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the single figure of the accompanying drawing, which is a diagrammatic illustration of an embodiment of the invention, there is shown therein a main transformer winding I which is provided with four taps 2, 3, 4, and 5. taps are connected to separate ratio adjuster switches 6 and 7, that is to say, the ratio adjuster switches each have relatively fixed contacts corresponding in number to the taps of the main winding and these fixed contacts are connected These 4 respectively to the diiferent taps. The ratio adjusters 6 and I also have their movable contacts for selectively engaging their fixed contacts and these movable contacts are connected by way of branch circuits 8 and 9 respectively to a conductor it! which leads to a terminal II for the winding l. The other terminal for the winding l is indicated at l 2.

The ratio adjusters 6 and 'l are ordinarily nonarcing duty type switches which are typically placed in a separate sealed compartment of the conventional transformer steel tank and they are ordinarily submerged under cooling and insulating liquid such as mineral oil. It is therefore necessary to provide some means for interrupting the current in whichever ratio adjuster is to be operated prior to such operation so that there will be absolutely no arcing at its contacts when its movable contact is actuated from one fixed contact to the next. This is accomplished by means of a split reactor [3 whose two halves are connected respectively in series in the branch circuits 8 and 9 and a switching system comprising a pair of non-arcing duty transfer switches l4 and I5 and three properly interlocked switches l6, ll and "3 which selectively perform the current interrupting or arcing duty of the system. Switch I! is connected into the circuit by means of an insulating transformer I9.

The transfer switch I4 is connected in the branch circuit 8 between the conductor l0 and one-half of reactor l3 and in series with the ratio adjuster 6. Similarly, transfer switch I5 is connected in the branch circuit 9 between the conductor Ill and the other half of reactor l3 and in series with the ratio adjuster 1. The switch i6 is normally closed and it is connected across the switches l4 and IS in series, that is to say, it is connected between the branch circuits 8 and 9 on the side of the reactor I3 to which the switches M and I5 are connected and not on the side of the reactor to which the ratio adjusters 6 and 1 are connected. Connected in parallel circuit relation with the switch I6 is a circuit containing the primary winding of the insulating transformer l9 and the switch IS in series. The switch I I is connected across the terminals of the secondary winding of the insulating transformer I9 and this secondary circuit is grounded as at 20. In this system ninety per cent or more of the entire arcing duty is performed by the contactor or switch [1. Consequently, the switches l4, l5, l6, and I8 may also be located inside the same compartment with the ratio adjusters, 6 and I and under its cooling is shown by way of example as being powered by i a motor 2I, although it will of course be understood that the mechanism could be hand-cranked if desired. The motor 2i may be started, stopped and reversed in any well known manner and it may be either manually controlled by push buttons or it may be automatically controlled in response to any suitable operating condition of the circuit of the main winding I. Through a set of bevel gears 22 the motor 2I drives a Geneva gear driver 23 having a pair of pins facing in L opposite directions and displaced 180 degrees from each other, which pins are adapted to engage respectively Geneva gears 24 and 25 which are mechanically connected through electrical insulating couplings 25 and 21 to the movable contacts of the ratio adjusters 6 and 'I. The Geneva gear driver 23 makes one complete revolution for one complete cycle of operation of the system. The switch or contactor I5 is driven by a cam member 28 through another set of gears 29 and, similarly, the switch I8 is driven by a cam 3d, the cams 28 and 39 being operated at the same speed so that they make two complete revolutions for each complete cycle of operation of the system. Driven by reduction gearing 3I from the shaft which drives the cams 28 and 3|] are another pair of cams 32 and 33 for operating respectively the transfer switches I4 and I5. These cams operate at half the speed of the cams 28 and so that they make one full revolution for each complete cycle of operation of the system. The main arcing duty contactor I1 is driven by a separate operating cam 34 at the same speed as the cams 28 and 30 so that it makes two complete revolutions for each full or complete cycle of operation of the system.

The operation of the illustrated embodiment of th invention is as follows: The system is shown in its so-called half-cycle or bridging position. This is characterized by having the ratio adjusters 6 and 1 connected to different, although electrically adjacent, taps. As shown, ratio adjuster G is connected to tap 2 and ratio adjuster I is connected to tap 3. The reactor I3 is in effect connected directly across or between the taps 2 and 3 through the ratio adjusters 6 and 'I and the transfer switches I4 and I5 so that it acts as an autotransformer and makes the voltage of the conductor It: and the terminal II equal to the voltage of a point on the winding I which is half way between the taps 2 and 3. Load current for the winding which flows through the conductor if) divides equally in the two halves of the reactor so that there is substantially no voltage drop in the reactor by reason of load current. There is, however, a current which circulates in the reactor due to the voltage difference between the adjacent taps 2 and 3 and this circulating current is limited by the magnetizing reactan'ce of the reactor l3.

Assume now that the motor 2! is operated in such a direction as to cause the cams 28, 3! 32, 33, and 3M and the Geneva gear driver 23 to rotate in the directions indicated by their associ ated arrows. The first thing that happens is that transfer switch I4 is opened by cam 32. There is substantially no arcing duty on this switch because switch I5 is still closed so that all of the current which has been flowing through the switch I4 from the upper half of the reactor I 3 through the conductor 8 will now flow through the switch I6 and then through the conductor 9 and the switch I5 and out through the conductor I0 as before. As the motor continues to turn, the next switch to open is the switch It. Here again there will be negligible arcing duty because the short-circuited insulating transformer I9 is connected in parallel with the switch I6 through the still closed switch I8. Consequently, the recovery voltage on the switch 15 will merely be the voltage drop of one-half the current for the main winding flowing through the leakage reactance of the insulating transformer I9 and obviously by well known design principles this leakage reactance may be made very low. Con tinued operation of the motor in the same direction will next cause the cam 34 to open the main arcing duty contactor IT. This opens the secondary circuit of the insulating transformer I9 and in effect interposes the magnetizing or exciting reactance of the insulating transformer I9 into the path for the current which flows through the ratio adjuster 6 and the upper half of the reactor I3.

At this point it should be explained that the insulating transformer I9 may either be a stepup or a step-down transformer; that is to say, it can either have a. higher secondary current and a lower secondary voltage than the corresponding quantities of its primary winding or vice versa so that the optimum values of current and voltage from the point of view of arcing duty for any particular contactor 'II may readily be obtained.

The recovery voltage on the arcing contactor I? is proportional to the voltage drop caused by the current in the ratio adjuster 6 flowing through the magnetizing reactance of the insulating transformer.

As the motor continues to operate, the cam 30 will next open the switch I8 and here again the arcing duty is relatively slight as this switch merely has to interrupt the exciting current of the insulating transformer I9. After the switch I8 has been opened it will be seen that the current in the branch circuit 8 is entirely interrupted so that ratio adjuster 6 may now be operated with no arcing at its contacts. Consequently the next operation is the movement of the ratio adjuster 6 counterclockwise one step so as to make connection with the tap 3. During this time all of the current of the windin I is being carried through the ratio adjuster I and the branch circuit 9 and this position of the system is known as its quarter-cycle position. This is ordinarily but a temporary position or condition of the system and the system is ordinarily not designed for continuous operation in this position. The voltage of the terminal II in the quarter-cycle position will not be quite equal to the voltage of the tap 3 because of the relatively high regulation in one-half of the reactor I3 through which all of the load current must pass. Consequently, the control of the system is ordinarily provided with an interlock (not shown) so that the system cannot be stopped in its quarter-cycle position but will continue on for a complete half cycle of operation before stopping. Therefore, the motor drive 2.I continues operating with the result that first switch l8 recloses, thus connecting the primary winding of the insulating transformer I9 between the branch conductors 8 and 9 or, in other words, across the switches I4 and I5 in series. Next the arcing contactor I1 recloses, thus in effect short-circuiting the insulating transformer, then the switch I6 recloses, thus in eifect shortcircuiting the leakage reactance of the insulating transformer I9 and finally the transfer switch i4 recloses. This has resulted in a complete rotation of the cams 28, 30, and 34, a half rotation of the cams 32 and 33 and a half rotation of the Geneva gear driver 2s and has placed the system in its full-cycle position in which the load current all flows through the tap 3 and divides equally between the two branch circuits 8 and 9 and the two halves of the reactor 53 and the voltage of the terminal i I is substantially equal to the voltage of the tap 3.

It will be noted that in any normal or continuously operating position of the system, that is to say, in either its half-cycle or full-cycle position, the primary windin of the insulating transformer i9 is short-circuited by the switch It so that there is no voltage across this primary winding. At the same time it will be noted that the secondary circuit of the insulating transformer I9 is grounded at Zii. Consequently, there is neither current flow through the switch I! nor is there any voltage to ground of this circuit. Consequently, the arcing contactor I! can be easily and safely serviced and even entirely removed from the system for such servicing while the transformer is in normal operation. Therefore, if desired, the arcing contactor I! may be made of the conventional draw-out connection type which is well known in switchgear practice. In other words, its electrical connections may be in the nature of plus and socket connections so that the entire contactor will be readily, in effect, plugged in or unplugged from the transformer.

A reverse operation of the motor drive from that previously described will of course first cause the opening of the transfer switch I5 and then the switches it, If, and i8 will open in the order mentioned which is the same order as has already been described, with the result that the current will be interrupted in the ratio adjuster and this ratio adjuster will then move clockwise so as to make connection with the tap 2. In other words, operation of the system in the opposite direction will cause a half cycle of operation so as to change the voltage of the terminal if from midway between the taps 2 and 3 to the voltage of tap 2 which is the opposite full-cycle position to that which was previously described in which the voltage of the terminal I I is changed to the voltage of the tap 3.

While there has been shown and described a particular embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and therefore it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a transformer winding having a plurality of taps, a pair of ratio adjuster switches for selectively making connection to said taps, a terminal for said winding, a pair of transfer switches connected to said terminal, a split reactor each half of which is serially connected between a different ratio adjuster and a different transfer switch, an insulating transformer, a disconnecting switch for connecting the primary winding of said insulating transformer across said transfer switches in series, and an arcing contractor connected across the secondary winding of said insulating transformer.

2. In combination, a transformer winding having a plurality of taps, a pair of ratio adjuster switches for selectively making connection to said taps, a terminal for said winding, a pair of transfer switches connected to said terminal, a split reactor each half of which is serially connected between a different ratio adjuster and a different transfer switch, an insulating transformer, a disconnecting switch for connecting the primary winding of said insulating transformer across said transfer switches in series, an arcing contactor connected across the secondary winding of said insulating transformer, and 'means for permanently grounding the secondary winding circuit of said insulating transformer.

3. In combination, a transformer having a winding, said winding having a plurality of taps, a pair fof liquid break ratio adjuster switches for selectively making connection with said taps, a terminal for said winding, a pair of liquid break transfer switches connected to said terminal, a split reactor each half of which is serially connected between a different ratio adjuster and a different transfer switch, an insulating transformer, a liquid break disconnecting switch for connecting the primary winding of said insulating transformer across said transfer switches in series, and an air break arcing contactor connected across the secondary winding of said insulating transformer.

4. A 1oad-rati0control system comprising in combination a multi-tapped transformer winding, a pair of ratio adjuster switches for selectively making connection with the taps of said winding, a pair of transfer switches having a common connection to a line terminal for said winding, a split reactor one-half of which is serially connected between one ratio adjuster switch and one transfer switch and the other half of which is serially connected between the other ratio adjuster switch and the other transfer switch, a switch connected across both transfer switches, an insulating transformer, a switch for connecting the primary winding of said insulating transformer across both transfer switches, and an arcing contactor connected to short-circuit the secondary winding of said insulating transformer.

5. A load-ratio-control system comprising in combination a multi-tapped transformer winding, a pair of liquid break ratio adjuster switches for selectively making connection to the taps of said winding, a pair of liquid break transfer switches having a common connection to a line terminal for said winding, a split reactor onehalf of which is serially connected between one ratio adjuster and one transfer switch and the other half of which is serially connected between the other ratio adjuster switch and the other transfer switch, a normally closed switch connected across both of said transfer switches in series, an insulating transformer, a liquid break disconnecting switch for connecting the primary winding of said insulating transformer across both of said transfer switches in series, an air break arcing duty contactor connected to shortcircuit the secondary winding of said insulating transformer, and a permanent ground connection "for "the secondary winding of said insulating transformer.

'6. An arcing duty switching arrangement for a load-ratio-control system comprising in Com? bination an insulating transformer, a switch for connecting the primary winding of said transformer between two points in said'system, an arcing duty switch connected across the secondary winding of said transformer, a third switch connected directly between said two points, and interlocking operating means whereby said switches are opened sequentially in the inverse order mentioned and :are closed sequentially in the opposite order.

'7. In a load-ratio-control system, a pair of points between which an electric current is to be interrupted, a normally closed switch interconnecting said points, an insulating transformer, a second normally closed switch connected across the secondary windin of said transformer, a third normally closed switch connected in series with the primary winding of said transformer between said points, and .means for opening said switches in the order mentioned and for closing them in the reverse order.

8,. In a load-.ratioecontrol system, a pair of points between which anelectric current is to be interrupted, a normally closed switch interconnecting said points, an insulating transformer, a second normally closed switch connected across the secondary winding of said transformer, means for permanently grounding one terminal of said secondary winding, a third normally closed switch connected in series with the primary winding of said transformer between said points, and means for opening said switches in the order mentioned and for closing them in the reverse order.

LOUIS F. BLUME. SALVATORE MINNECI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,664,325 Shivers Mar. 27, '1928 2,209,126 Littlefield July 23, .1940 

